This invention relates to the use of vanadium oxide nanotubes as electrode material in a rechargeable lithium battery.
Vanadium oxides have a long history as potential electrode materials for rechargeable lithium batteries due to their ability to insert large amounts of lithium [Winter et. al., Adv. Mater., 10,725(1998); Chung et. al, J. Power Sources, 84, 6 (1999); Shembel et. al, J Power Sources, 81-82, 480 (1999); Lee et. al., J. Electrochem. Soc., 142, L102 (1995); Pistoia et. al., Solid State Ionics, 13,311 (1984)]. Different synthesizing and preparation methods have been developed to achieve higher specific capacities and longer cycle life [Chung et. al., J. Power Sources, 84,6 (1999); Shembel et. al, J. Power Sources, 81-82,480 (1999)]. Promising results have been reported for amorphous low-crystalline materials e.g. V2O5 xerogels and aerogels [Lee et. al., J. Electrochem. Soc., 142, L102 (1995]. Another material that has demonstrated large capacities as a cathode material is the vanadate LiX+1V3O8 [Winter et. al, Adv. Mater., 10, 725 (1998); Shembel et. al, J. Power Sources, 81-82, 480 (1999)].
The synthesis of vanadium oxide nanotubes (VOxxe2x80x94NTs) by a ligand assisted templating approach has recently been described by Spahr et al. [Angew. Chem. Int. Ed. Engl., 37,1263 (1998)]. The tubes consist of several vanadium oxide layers, commonly in a scroll-like arrangement, separated by structure-directing agents (templates). The tubes can be up to 15 xcexcm long and consist of as many as 30 vanadium oxide layers. The outer and inner diameters vary between 15 to 100 nm and 5 to 50 nm respectively. The size depends on the precursors chosen for the synthesis and can therefore be controlled in a rough manner [Krumeich et. al., J Am. Chem. Soc., 121, 8324 (1999)].
The synthesis is performed with e.g. primary alkylamines as templating molecules. The embedded amine molecules can then readily be exchanged by various metal cations, i.e. alkaline, alkaline earth and transition metals, under preservation of the tubular morphology [Reinoso et. al., Helv. Chim. Acta., 83, 1724 (2000)]. This property gives a unique opportunity to design tailor-made functional materials. However, attempts to substitute the amine by lithium-ions have so far not been successful [Reinoso et. al., Helv. Chim. Acta., 83, 1724 (2000)].
The investigations into these types of inorganic nanotubes, e.g. dichalchogenides and oxides, has increased rapidly over the last decade [W. Tremel, Angew. Chem. Int. Ed., 38, 2175 (1999)]. Redoxactive tubes, containing transition metals, are naturally of fundamental interest for both catalytical and electrochemical purposes.
A method for the preparation of separable vanadium oxide nanotubes is discussed in PCT publication, WO9826871 by Nester et. al., which recently issued as U.S. Pat. No. 6,210,800.
Spahr et. al. [J. Electrochem. Soc., 146, 2780-83 (1999)] teach the electrochemical characteristics of vanadium oxide nanotubes, studied with electrodes consisting of a mixture of vanadium oxide nanotubes and teflonised carbon black, each representing 50% of the mixture. Cyclic voltammograms of templated vanadium oxide nanotubes recorded at 50 xcexcV/sin 1MLiClO4 in propylene carbonate, displayed a stable specific charge of about 120 mAh/g, obtained for the Li insertion during the first five cycles of voltammetric measurements. Thereafter, the specific charge gradually decreases with increasing cycle number to less than 100 mAh/g after ten cycles.
The present invention provides an improved vanadium oxide electrode, which employs improved methods of electrode synthesis, cation exchange, and choice of electrolytes than those taught in the prior art. Numerous differences exist between the present invention and the teachings of Spahr et. al. including but not limited to, the use of hexadecylamine as templating molecule by Spahr. et. al., compared to dodecylamine used in the present invention, use of a higher percentage of vanadium oxide nanotubes in the electrode of the present invention compared to the teachings of Spahr et. al., and most importantly a choice of electrolyte different from the one taught by Spahr et. al. The present invention therefore, represents an improvement over the prior art.
According to the present invention, an electrode comprising vanadium oxide nanotubes is provided. Further provided are the method of making and the use of the electrode in a rechargeable lithium battery.